Nucleon-nucleon bremsstrahlung: An example of the impossibility of measuring off-shell amplitudes

Abstract

For nearly fifty years theoretical and experimental efforts in nucleon-nucleon bremsstrahlung (NN$\gamma$) have been devoted to measuring off-shell amplitudes and distinguishing among various NN potentials on the basis of their off-shell behavior. New experiments are underway, designed specifically to attain kinematics further off shell than in the past, and thus to be more sensitive to the off-shell behavior. This letter shows that, contrary to these expectations, and due to the invariance of the S-matrix under transformations of the fields, the off-shell NN amplitude is as a matter of principle an unmeasurable quantity in NN$\gamma$.

9 pages, Latex, using RevTeX; Minor wording changes, title changed, version to be published in Phys. Rev. Letters

References in corpus (1)

• On electromagnetic off-shell effects in proton-proton bremsstrahlung

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